Alternative to X-Rays Uses Visible Light

Below:

Next story in Science

Some day we may not need X-rays to see inside people, thanks to a
new way to decipher light that passes through opaque surfaces.

Normally visible light becomes too scattered to detect after
passing through opaque surfaces. But scientists in France have
developed a way to reconstruct images from light passing through
such surfaces by deciphering just how the material makes the
light scatter.

In the short term the research will help improve the strength of
telecommunications signals and fiber optics cables, but years
from now the technology could supplement or even replace
traditional ultrasounds for baby imaging and X-rays for weapons
detection at airports.

"It's like putting a flashlight behind your hand," said Sylvain
Gigan, a co-author of the recent Nature Communications
and a scientist at the Institut Langevin in Paris. "You cannot
see an image, but you can still see a faint glow."

Imagine that there was an image over the top of a flashlight. As
the light passes through your hand the image is destroyed; all
you see is a faint glow. But using the new method pioneered by
the French scientists, they can collect the light and extract an
image from it.

Their experiment contained three key pieces of widely available
technology: a green laser as the light source, a light modulator
(which is often used in projectors), and a charged coupled
device, the technology used in many digital cameras.

The laser created the light, which was sent through the
modulator, and illuminated the image (in their tests, a rose).
The green light bounced off the image and through a glass slide
that was painted white, which scatters the light in all kinds of
different directions.

Ordinarily that would be the end of it; the image captured by the
digital camera would be blurred beyond all recognition. The
French scientists got around this limitation by taking picture
after picture of the blurred image, and then applying a program
that accounts for how the light is scattered by the white glass.
That way they could reassemble a grainy image of the flower.

"When light hits a glass of milk, a cloud, or our tissues, some
of it is absorbed, but most of it is scattered," said Gigan. "You
would think that this light is scattered beyond recovery, but
it's not."

It's not imaging as we are used to seeing with X-rays or
ultrasounds, said Changhuey Yang, a scientist at Cal Tech
familiar with the new research. The image that comes through is
grainy and can only work through think opaque surfaces.
Nonetheless, Yang said it was "fascinating" that the French
scientists could detect an image through a opaque medium.

When doing traditional imaging, like using X-rays to find hidden
weapons at airports, "we assume that we know nothing about what
is on the other side," said Yang. "In this scenario, this is not
the case."

In other words, the French scientists knew what image is supposed
to come through. If it were a totally random image coming through
the glass it would be much more difficult to detect with their
existing technique.

That should be possible one day, said Gigan, but right now its
not. When it happens however, the technique could lead to a huge
variety of applications.

"What we showed can be adapted to any wavelength," or any kind of
wave, said Gigan. At first the technique could help cleanup noise
in telecommunciations signals or fiber optic cables. Eventually
however, the French scientists hope to adapt their technology to
other see-through technologies, such as X-rays or ultrasounds.